This paper addresses the aspect-oriented specification of systems by considering different aspects of a simple stream example. It is shown how these aspects can be expressed in different formal languages if required. By using an underlying common semantics to the different languages, it is then possible to compose the aspects in order to perform analysis of either the interaction of aspects (c.f. feature interaction) or the overall system behaviour. Our composition process is analogous to the aspect-weaving of aspect-oriented programming and our multi-way synchronisation of events (either explicit or implicit) mirrors the join-points of a program. We also briefly describe our Composer tool suite that supports our aspect-oriented approach.